1. Field of the Invention
The invention relates to a device and a process for treating a chemical substance by heating under pressure comprising at least one container which can be closed so as to be pressure-proof and serves to accommodate the substance.
Devices and processes of this type are used for example for the decomposition, elemental analysis or dehydration of sample material arranged in one or more container(s) by heating, the pressure in the containers increasing as a result of the heating.
DE 38 18 697 C2 has disclosed a heating device for heating sample material in pressure-proof sample containers composed of a housing and a cover. In this device the heating power is reduced as a function of the inner pressure in the container. The pressure indicator used for this purpose is formed by a slide which is displaceable via a membrane by the pressure in the container, and a pressure sensor or switch which is connected to a control circuit for the heating power of the heating device. Preferably, the heating device is formed by a microwave oven.
Furthermore, DE 39 19 601 C2 describes a device for the decomposition by acids of a substance for elemental analysis in a microwave field generated by a microwave oven under controlled pressure in a sealed decomposition vessel. In the device disclosed therein, which exclusively comprises parts made of microwave-permeable material, a microwave-permeable, measured value sensor on the one hand is actively connected to a pin whose vertical upwards movement is a gauge of the increase in pressure in the decomposition vessel, or is detachably connected thereto, and on the other hand is connected to a pressure display device or control device for the microwave heating arranged outside of the microwave oven. The microwave-permeable measured value sensors used are those which operate mechanically via a lever, hydraulically, pneumatically (in each case in contacting fashion) or optically (in non-contacting fashion).
The optical measured value sensor proposed in DE 39 19 601 C2 consists in the simplest example of an optical transmitter and a receiver, which latter receives the light beam emanating from the transmitter until the beam path is interrupted by the upwardly moving pin. The absence of the received signal then triggers the switching off of the microwave heating. Equally, a reflector can be arranged at the upper end of the pin so that upon the overshooting of a specified pressure, light is thrown back from the reflector onto the receiver and the microwave heating is thus switched off.
As in the described prior art all the parts must consist of microwave-permeable material, it is not possible to use elements which are actually more efficient, for example for sealing the container and for the pressure detection.
Additionally, the known pressure detection systems do not permit adequate control of the reactions occurring in the containers. In particular in processes for the decomposition of organic substances, extreme exothermic reactions take place which under normal circumstances go totally out of control and are associated with an extreme rise in pressure and temperature which frequently leads to the destruction of the containers. It is not possible to damp these reactions in association with normal pressure detection as, at the instant at which the energy supply is switched off, upon the overshooting of a predetermined pressure limit value in general a certain part of the sample material has already reacted and the reaction continues automatically and in an uncontrolled manner.
The aim of the invention is to provide a device of the type described in the introduction with an improved pressure monitoring system in which moreover more efficient components composed of microwave-absorbent material can be used.
Additionally, a process is to be provided which, by virtue of the pressure monitoring, facilitates improved control of the reaction occurring in the containers so that the reaction can be substantially prevented from going out of control and the reaction can be continued in controlled fashion at a constant pressure.